1. Field of the Invention
The invention relates to a method for controlling at least two physical properties, decisive for the quality of the finished smokable article, of a material rod of filter or tobacco material for the production of smokable articles, particularly in the filter and cigarette industry.
2. Description of the Prior Art
Although similar problems occur with other smokable articles, the complexity of problems will be discussed only in conjunction with the manufacture of cigarettes.
In the manufacture of cigarettes various techniques are used to permit the continuous control of the physical properties of the rod of tobacco fibres during the cigarette manufacture and thus finally of the corresponding properties of the finished cigarette. It is, for example, known to determine the density of the rod important to the weight constancy of the cigarette and corresponding in turn to its weight, to compare the actual value determined with a reference or desired value and to control the formation of the rod in dependence upon the result of the comparison (German Offenlegungsschrift No. 22 08 944). For measuring the density, for example, the absorption of radiation in the rod of tobacco fibres can be employed, in particular beta radiation or microwaves. German Offenlegungsschrift No. 27 28 797 further discloses a method of manufacturing cigarette filters in which the draw resistance of the filter material or two is determined, compared with a desired value, and the result of the comparison is used for the filter tow supply; the tow supply is controlled so that the pressure drop across the measured tow remains substantially constant.
A further method is known from published European patent application No. 0 032 399, the humidity, mass, machine speed and the hardness of a rod of tobacco fibres being determined for the control; the measured hardness value is corrected by means of the other parameters, i.e. humidity, mass and machine speed, thus giving a corrected actual value which is compared with a desired value. Dependent on the result of this comparison, trimmer discs, which in the formation of the rod set a predetermined height of the tobacco rod, are adjusted.
Suitable sensors for detecting the harness of the tobacco rod are apparent from German Offenlegungsschrift No. 33 06 543 and German Offenlegungsschrift No. 34 04 635.
Finally, prior German patent application No. P 36 13 957.2-23 corresponding to U.S. Pat. No. 4,771,794 describes a method for controlling at least two physical properties, decisive for the quality of the finished product, of a rod made from smokable material, in particular in cigarette manufacture, wherein the actual values of said properties are detected, the particular differences between the actual values and the associated desired values are determined and finally from the determined differences control signals are obtained; these control signals are compared with each other so that the instantaneously largest control signal can be passed to a single actuating element for the mass flow of the smokable article. The control signals can be obtained from the hardness of the rod of smokable material, the draw resistance and/or the weight of the rod, and compared with each other.
This makes it possible to adjust the essential quality parameters of a smokable article, in a cigarette this is its draw resistance and hardness, very exactly to the optimum value and to rapidly recover the optimum state even with disturbances in operation.
In a rod-forming machine as used both for cigarette and filter manufacture a number of medium-term to long-term disturbances occur which can greatly influence the essential product and quality parameters, that is weight, hardness, draw resistance and diameter.
These disturbing influences include in a cigarette machine the humidity or moisture, the composition and the properties of the tobacco mixture as well as environmental influences, machine settings and the tolerance fluctuations due to the wear of machine parts, in particular format belt and format parts, and in a filter-making machine include the material properties of the filter material, as a rule cellulose acetate, the plasticizer content (content of triacetines) of the filter material and also the environmental influences, machine settings and wear of machine parts. The major environmental influences include the temperature and humidity whilst as main machine setting acount must be taken of the speed of rotation and thus the conveying speed.
In the regulation or control of the manufacture the actual values must, for example, be determined for the weight and/or the hardness and/or the draw resistance and/or the diameter by corresponding sensors and compared with predetermined desired values to bring the production finally to the optimum state.
However, this is problematical in that the individual parameters depend both on each other and on the disturbing influences explained above so that the adjusting of the particular desired values, in particular when starting the machine, is problematical.